In a picture-in-picture (“PIP”) television receiver, the television takes video from at least two input sources and creates a single image. The image created by a PIP module is composed of a main part that occupies the full dimensions of the image, and one or more PIP parts that are scaled to occupy only a small portion of the overall image. The PIP part is typically wholly contained within the main part of the image. The PIP part of the image may be arbitrarily positioned anywhere within the main picture. The PIP part of the image may also be arbitrarily sized (or resized). In the multi-window display mode, also known in the television industry as picture-out-of-picture (“POP”), two or more non-overlapping display regions are arranged on the screen in a mosaic pattern. Each display region contains video from an independent video source, and can be of varying sizes or shapes. The preferred implementation of the multi-window feature limits the number of regions to two, equal-sized panels (panel 1 and panel 2) that are displayed side by side. In effect the screen is comprised of two main regions.
It often occurs that users, after watching a program on a certain channel for a while, want to temporarily watch one or more other channels. This habit is called ‘zapping’ channels. For example, when there is a commercial break on the original channel, the user may zap to other channels to catch some interesting bits of programs there. While zapping other channels, the user needs to check whether the commercial break has ended and if so, will resume watching the original channel.
U.S. Pat. No. 5,900,916 describes an apparatus for presentation of images from multiple sources on a monitor at the same time, wherein a main picture has overlayed on it a PIP occupying a minor portion of the main picture. In a so-called review mode, the PIP displays the channel which had been displayed on the main picture prior to the channel change. In this way, a user can watch the previous channel when zapping. When the user switches to yet another channel (i.e. a third channel), the original channel (i.e. the first channel) will not be displayed anymore. This means that when the user is zapping, for example during a commercial break on the original channel, he will not be able to notice the ending of the commercial break, since he can not see the original channel on the screen after two channel changes.